Conversions... what's the problem?

the main PRACTICAL disadvantage is that the bottom bracket will be lower —*meaning you'll be more likely to get pedal strike. The solution is to use short cranks, but you'll get less leverage and so it will be harder work.

Oh and track drop outs make it easier to tension the chain, but only marginally.

There is also the fact that the geometry will be slacker, which will affect the handling— but this is a matter of personal preference.

The only other objections will be aesthetic - I personally think it's a bit sad when people 'slay' lovely road frames to make them into 'fixies'.. but each to his own. As long as you don't saw off the cable guides and mech hanger you'lll be able to convert it back when you get a 'proper' track bike

As Dan says, a major problem is that the bottom bracket is too low, add to this the short cranks and you have a recipe for serious ligament, muscle and knee joint problems as you inevitably spedn a lot time grinding - pedalling far too slowly. 90 -110 per minute and NO slow turning starts. I will be dead by the time all the fixed/singlespeed trendies are costing everyone a fortune in NHS payments but my kids will have to pay. So just don't do it.