All Grain Future Expansion

What is the disadvantage to having a 10 gallon HLT for 10 gallon brew batches? Blichmann Engineering recommends that for 10 gallon batches you use a 15/15/20 setup. Would it be a bad idea to have a 10/15/20 setup and heat your strike water from you MLT?

I'm just getting into All Grain Brewing, and I'm thinking of starting with a setup like this: 10(cheap kettle)/5 gal beverage cooler/10 blickmann.

My plan would be upgrade my MLT to a 15 gal, then move my brew kettle to my HLT when I eventually purchase a 20 gal brew kettle.

Would it be a bad idea to use a 15 gal MLT for only a 5 gal batch? I would have to do this while my system is at 10/15/10 until I can get a larger brew kettle...

Is this a bad plan of action? Thanks for the input.

IMO, I would go with a bigger cooler for the MLT (60Q Coleman Xtreme at WM) and keep the 10 gallon brew pot. Then again, I'm fine with doing 5 gallon batches.

You don't need 10 gallons of hot water to mash-in. An hour mash is plenty of time to heat more water for sparge.

Okay, thanks for the help guys!