There's a difference of opinion about the effectiveness of split filter printing. A search will turn up a bunch of threads...

I use it because I think it gives me more control over the final image, but many would argue I'm foolin' myself. The only way to know if it is for you is to try it. Start with a full sheet of paper, and do a test strip with the No.4 filter. Find the time which gives you the shadow value you want. Then, expose a full sheet with that time, and do a test strip with the No.0 on that sheet. Find the highlight value you want. Then, combine the 2. If your chosen shadow exposure is 10 seconds, and your chosen highlight exposure is 20 seconds, expose your print for 10 sec. with the 4, and 20 sec. with the 0.