For Find Familiar:
…as an action, you can see through your familiar's eyes and hear what it hears until the start of your next turn, gaining the benefits of any special senses that the familiar has. During this time, you are deaf and blind with regard to your own senses. (PHB pp 240)
Because the senses you gain are only those of sight and hearing, and sight and hearing are the only ones explicitly called out as lost, my thinking is that, while your sight and hearing are replaced with that of the familiar, you would still have your other senses, i.e. touch, balance, etc. Your familiar can see you and your surroundings, so you wouldn't be hampered. Would this be correct?
Assuming this is true, you could then use your familiar-vision to see unseen opponents. My thought here is having an owl (darkvision) or a bat (blindsight) as my familiar, so that I can see enemies in the dark, or who are invisible. This would take away their advantage (if they can see me) and, though I've used my action in order to see, it would allow me to make Attacks of Opportunity against them with advantage. (I can take Move and Bonus actions normally) Also, if I can cast Beast Sense, which has identical sensory alterations but lasts much longer, I can make normal attacks with advantage.
Additionally, assuming all of this is true, if I spend a turn looking through my familiar's eyes, could I then know where my opponents are on my subsequent turn in order to attack them?
Best Answer
I had this exact issue when DMing recently. The way I ended up playing it was by allowing to try to move but every motion and action required an intelligence check DC 10 as he would have to deduce the direction he needed to move etc based off the altered and changing perspective of his familiar. However when he had the bat land on his head so its perspective was the same as his own I lowered the DC to 2 because now it was just a slightly different sensory experience. This seemed to work really well and the players thought it was fair.