A sub domain has less wight in indexing with google .
In the old days, you could get indexed but that all over, since whois become public ...
The main domain ,then a folder name ,is much better ,and get indexed.
Sub domains still get used ,but usually pointing to pages the admin wants to get to for quick access , not used heavly these days for public websites.
There no reason you can not use a sub domains , there just not seen as safe buy visitors .
Classed as very unsafe and spammy
http://money.mywebsite.com
To this
http://www.mywebsite.com/money
As you can see there a huge diffrence and ppl do take notice of urls and the way they look.
Good luck
