ALV with and without SLIS

What is the difference, if we create a ALV program using FMs for Grid Display, with and without declaring TYPE-POOLS : SLIS.

If i develop a ALV(FMs) program by declaring the types from FM's it is working fine.

If i declare a internal table using it_fcat TYPE STANDARD TABLE OF slis_fieldcat_main(type from SLIS) and did not use declaration TYPE-POOLS : SLIS. This is also working fine.