What's the difference between Free Pay as you go sim & 12/24 Months Contract Mobile Broadband?

[MRX_001]

Just like it says in the Title, 

What's the difference between "Free" Pay as you go sim which can be ordered for free from the website & a 12 or 24 Months Contract Mobile Broadband SIM? 

I'm planning to get an Advanced SIM contract to use my phone as a personal hotspot and I will be playing Online Games on my laptop. (Example: Call of Duty Warzone, Battlefield etc) 

Regards

[sc1999]

A PAYG sim unlimited costs £35 per month a 24 month contract sim £25 before shopping around.

[sc1999]

You need to do your sums as PAYG may cost a lot more than an unlimited contract if you are gaming.