I suspect the author in that sentence hesitated between often and most of the time: he wanted to indicate that it was helpful very, very often; but he didn't want to go so far as to say that it was helpful more than 50 % of the time, and so he chose a somewhat cowardly expression in between. I think he would have been better off choosing either often or most of the time, or perhaps very often, though I don't think the added intensity of very is really necessary.
Most of the time is an expression indicating that something happens more often than not, usually much more often.
Much of the time I would normally only use where you could not substitute often, a simpler word, which is the case especially when it is about a large chunk or chunks of a period, not merely a frequent number of times.
They arrived early at the aeroport. They had wanted to spend their final hours in romantic embrace, but they were busy looking for the right papers and documents much of the time.
This means that a large part of this time was spent looking for papers, but "large" could be anything from 1 % to 99 %; if I used most of the time, it would mean that more than half of the time was spent on it.
As a crude rule of thumb, if you:
- spend something to do something
... then you spend it before you get or achieve the second thing. Here are some examples:
- We spent a lot of money to ensure the highest quality of workmanship.
- It's time to spend money to create jobs.
- There's no hiding from the fact we spent money to get players in.
In these instances, the infinitives are infinitives of purpose. In other words the infinitive tells us the goal of the spending activity.
In contrast if you:
- spend something doing something
... then you spend it as you are doing it. In other words the spending something and the doing something are happening at the same time:
- We spent a long time cleaning up after the party.
- We spent a lot of energy exercising and fretting over our physical condition.
Notice that in these instances, the -ing-clause tells us how we spent something, not necessarily why we wanted to spend it. Consider the following examples:
- We spent a lot of time getting nowhere
- We spent a lot of time being chased be photographers
Here we did not spend the time with the goal of not making progress or with the goal of being chased.
Gerund participle forms of verbs often indicate simultaneity, in other words they show that two actions are happening at the same time:
- He was run over crossing the road.
- Speaking with his mouth full, he asked me what I'd been doing.
The Original Poster's Question
*We spent a lot of time to shop.
We spent a lot of time shopping.
The Original Poster needs to use the second sentence here. The reason is that the spending time happened concurrently with the shopping. The two activities happened together.
Best Answer
Yes, myself (or any other intensive pronoun) can be used after the verb (e.g. He learned it himself) with a meaning slightly differing from that of using it directly after the pronoun (e.g. He himself learned it). The extra himself in the latter emphasizes that it was indeed he, and no other, who learned it; whereas in the former (pertaining to your question), it emphasizes that he learned it by himself, without significant help.
Intensive pronouns work as well with other verb tenses (such as present tense), but when there is no other direct object (e.g. it in learning it yourself), the intensive pronoun (yourself) becomes ambiguous. Therefore Learning yourself is good is at best an ambiguous sentence because yourself here can easily be interpreted as a stand-alone noun, resulting in a meaning of Learning about yourself is good.
Learning yourself doesn't go against grammar, but it is pitifully ambiguous, and I would advise against it. If you put an intensive pronoun after the verb, make sure there is a clear direct object or modifier, or else the pronoun itself will likely be viewed as the direct object.