Hello Thomas...
Happy to hear about your shared appreciation for catenary...

There are many reasons why you might want to occasionally run your e-loks without catenary power.
1) If you are using analog system, you can run two cat loks on one section or circuit, one from Catenary, the other from track.
2) You may have a issue, or breakage with your catenary and you need to test or run your loco to check and repair catenary.
3) You may have issues with the loco itself, a broken pantograph, or a connection issue and you may want to test it on track without catenary.
4) Putting the loco on and off track without catenary is also easier... your staging area could be without catenary and if the switch is accessible without removing the loco from the track, then you can run it over to the catenary section and change over the switch.
IMHO Functioning with slider is also easier with digital too.
I would only remove the slider if it is not one of the older soldered on type, unless of course, you cannot stand the slider sound or it really bothers you. Resoldering may be a hassle.
Advantages of removing the slider:
1) You save on sliders (but wear down pantographs.)
2) Less hissing sound.
3) Less chance of slider issues in general, such as twisted slider getting caught on pukos (middle rail bumps)
4) Less visual distraction to some.
Frankly I have grown to find the visuals of the slider charming as it is particular to the Marklin 3 rail system and brand.
That said, I do love having our analog layout with real catenary power. It has made for great conversation about the "live wire" at train shows we take our layout to, and also fun capabilities of running one train with cat and the other steam lok say with track.
Marklin insulators for catenary are also interesting to work with.
Are you planning to use the classic Marklin catenary of the past, or new wire catenary?
If you plan to use it live, the older stuff is much more stable, easier to work with and makes better contact with the pantograph, unless you are experienced at setting up the wire type catenary.
(Please anyone correct me or add to this, because my experience as yet is only with older type catenary. I have a big box of Sommerfeldt catenary posts, masts of all kinds that I got in an amazing deal 2 years ago that I hope to use on our new layout...
but expecting it to be a challenge as I continue to read about it.)
I look forward to seeing your progress with catenary and am willing to encourage with what I know in your endeavor.
Cheers and welcome to the Forum,
Mark
Originally Posted by: hennabm 
....[.....].....You can remove the underside slider if you wish as it is not needed for catenary operation. I know this because when I was a lad my 3011 lok slider broke off and the only way I could run it was from the catenary.....[.....].....