I applied for a standard UK Visitor Visa, which I later got after 15 working days. Here's my experience;

I opted for self service and uploaded all the requirements i deemed were necessary. this includes;
-Letter of Appointment
-IELTS Results
-Unpaid Booking. com accomodation reservation
-MBBS cert
-2 Bank statements
-CV
-Cover letter
-Confirmation of exam I'm going there to write

I submitted my online application around 25th May, and while it was stated that the only printout I need to bring with me in addition to my passport, is the Checklist and Proof of payment of any other TLS services purchase e.g Super Priority etc...well, thats not entirely true.
Anyway, lemme break it down into points;
1. You can walk in earlier than your scheduled time of appointment e.g if your appt is 2pm you can still come in the morning and they'll attend to you. So its not strictly by your appt time.
2. If you opt for self service, please photocopy the data page of your passport before going in there. Even though they don't mention it among the things to bring, i believe this is their cunny way of extorting people. Why did i say so? They'll ask you if you have the data page photocopy, if you dont, they'll ask you to pay N400 to do it for you (it's compulsory), and they dont collect cash, it has to be with Card. So i handed the lady my card, and tried the transaction but it failed. She tried again, it failed. She was like oga are you sure you have money in your account? The kind of look i gave her made her shut-up. She attempted it the 3rd time and it went through. But guess what? I was debited 3 times for all the successful and declined transactions, and I didn't realise it till i came out of the building coz we were asked to turn off our mobile phones. That's not even the annoying part.
What annoyed me most was the fact that the data page print out is USELESS to both you the applicant and them also, coz after they photocopy it they'll give it back to you to go back home with it. It has no use! Not even when collecting back your passport. Coz I collected my passport without them asking for the printout of datapage. So they practically wasted my N400 x 3= N1200 for nothing , money I could've used to buy data. What's even more annoying is that on the receipt of the payment is says N50 for the actual photocopy and N350 for SMS services. I was like sms to who? about what?
I really believe its their little way of extorting people money especially those that opted for self service and not assisted service.
So if you belong to the former, do your self a favour and photocopy it for atmost N20 before going for you appointment.

Just my little rant.