it's a personal preference. there are a lot of benefits when using a refugium on a tank. it's adds to the total water volume of a tank and in turn making the tank more stable. if you decide to use a microalgae, the algae can control nitrates and phosphates...it can also act as a breeding ground for smaller organisms such as copepods. you can run a reverse photoperiod using a small lamp over the refugium and in turn creating more stable PH levels between day and night. you can also use a refugium as a way to hide mechanical or chemical filtration mediums so not to deter from the beauty of the tank. all of the above mentioned are obviously positive benefits to the well being of the tank.
with that being said, from personal experience i have used refugiums on tanks before and some without. i have also used an aquaclear 70 before as a refugium with no problems, you are limited with internal space though. i personally believe you have nothing to lose if you employ one onto your current tank, if anything you'll gain experience utilizing a refugium into your current set up. as of right now i have a standard ten gallon with no refugium or sump...i am however contemplating the idea

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i hope that helps,
jonathan