If you arrive really early in the day you’ll probably want to try and check in early. We do! Some resorts, like Aria, let you check in early if they have available rooms; other resorts have policy whereby you cannot check before a particular time: for some it’s 2pm, for others it’s as late as 3.30 or even (in the case of Caesars Entertainment Vegas resorts) 4pm! This annoyingly late check in is due to the fact that those resorts apply a fee if you check in earlier than 4pm.
The reality is that most resorts do not operate at 100 per cent capacity, so it’s possible that they will have rooms available no matter how early you arrive; it is therefore totally discretionary if you are allowed to be the exception and therefore allowed to check in early. If so, you will not have the choice of a room, you’ll just have to take whichever they have available.
Some Vegas resorts don’t even let you leave the bags with the bell desk whilst you are waiting to be checked in early (we had a bad experience like this at Plaza in downtown Vegas); but some not only let you place your bags with bell desk, but they will even allow you to do a virtual check in, which means that all you have to do is come back a little later on when your assigned room is ready, but you will be assigned a room already (and therefore you will have had a wide array of choices).
As long as you can leave your luggage with bell desk, checking in early is great, since you can immediately go on and enjoy Vegas, or go to a lounge or a cafeteria and relax, or (if your resorts provides free wireless Internet), sit down in the conference areas and access the Internet. Or, of course, you can go gambling (I would not reward a resort with early gambling early unless they were very accommodating at check in).
Some resorts have areas where you can sit down at relax near the reception area (and access the Internet) at no charge, such as Main Street Station; but others are very ‘cheap’ (even if they are expensive resorts) and do not allow such ‘luxuries’ (or rather, good customer service). Phone them or write to them in advance (I like to have everything in writing) so you can be prepared, or opt out of a specific resort if necessary. If you check in as VIP or invited guest, you can talk to casino marketing and see what they can go for you; however, the VIP check in area often provides comfortable seats and free beverages, so you could take advantage of that.