Requests are for something extra than the category you booked. Unfortunately, over the years, Disney has realized they can finally create new booking categories to encompass the vast amount of requests over the years and people are more than willing to pay for it (case in point, two years ago, the mods got a bunch of new categories).
Most requests are:
floor level(first, second, third) some prefer to be on first floor with quick access to a pool; some prefer to have no one above them, some people prefer not to walk out of their room and encounter a critter.
Close to transportation: while preferred is a booking category close to the main transportation, some resorts have multiple bus stops and you can request being close to that area.
Close to pool: obvious choice.
Far from pool: don't want to be in a noisy area.
Adjoining rooms: multiple parties wanting to be in rooms next to each other.
Connecting rooms: want to have a door between so they can share room; keep eye on children, etc.
Upgrades that you are referring to (the discussion always comes around to this) are few and far between. They are usually based on circumstances that are beyond your control and you never know who's going to get one, if any. They may be anywhere from refurbishments in the resort that takes rooms out of inventory, a family that had to stay an extra day due to weather that they cannot get home, rooms with maintenance issues, overbooking at another resort that needs rooms, etc.
The worst way of getting an upgrade is asking for one. You will most likely be perceived as trying to get something you didn't pay for; remember there are a lot of other people out there, that are also celebrating special occasions that paid for the level of room they wanted and they are going to get it.
If you do ask for an upgrade, you will most likely be quoted the difference in price and it will be based on the highest rack rate for the new, upgraded room - and you will lose any discounts you may already have on your existing reservation. You will have to decide if it is worth it to you.
Best to book what you want or be happy with what you have - and don't set yourself up for disappointment.