Most importantly it will delibaratly slow down execution if you exceed some limit on the number of code lines ,I think its a couple of thousand statements.It wont let you have mixed VHDL and verilog designs,its limited in some of the libraries you can use,specifically the VITAL2000 libraries and its got one or two new design views in the full version but for a beginner those things shouldnt hold you back
the microblaze and picoblaze are all good in that they do what they say on the tin.