A sliding compound allows you to do all the cuts that you can do with a normal compound saw. But it allows you to do it with up to a 12 inch board. Now that 12 inch cut is at 90 degrees only and usually at the depth that the blade can cut. That depth is dependent on weather you have a 7 1/4 diameter blade, 8 1/4 inch blade or a 12 inch blade.
I used to have a table saw, a radial arm saw and a 71/4 inch compund saw. I used the table saw 65% of the time. The compound saw 30% of the time and the radial arm saw 5% of the time. Buying the sliding compound saw. I got rid of the radial arm saw, and have not missed it. The radial arm saw has the most lawsuits of any woodworking tool.

Dave

__________________
1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car