Just stumbled on this part I’d never seen before and having hard time to figure real usefulness and efficiency for hard materials like wood or aluminum !? Any users of these and or feedback ?
Feels more fitted for blade cutting of soft sheets like paper, fabrics or leather, Am I right ?
http://www.aliexpress.com/item/New-0-8kw-1-5kw-Spindle-Holder-65mm-Clamp-Plate-For-DIY-CNC-Router-Material-Auto/32329569546.html?spm=2114.01010208.3.94.5OKANx&ws_ab_test=searchweb201556_9,searchweb201602_4_505_506_503_504_10034_10020_502_10001_10002_10017_10010_10005_10006_10011_10003_10021_10004_10022_10009_10008_10018_10019,searchweb201603_1&btsid=294a2945-0e29-4464-8626-f9a634d0a0e8
Looks like it would be great for thin plywood or metal. Also for cutting specific depths like on the multi color sign material.
I would also guess it is good for PCB milling and probing the PCB when you are autolevelling beforehand. However it feels a bit too big for being useful in a smaller setup as you have to keep so much more clearance from clamps and so on…
+Peter van der Walt actually you led me to it ! It’s in the same shop you pointed for 65mm water cooled spindle 
@David_Kirtley indeed it could counter horizontal constraints which may raise thin aluminum or wood sheets.
Having no experience with these, I don’t understand the benefits in the second use case… Would you please educate me ? 
They have plastic material that has two colors to make signs. You cut to a certain depth to expose the other color. If the material is not held flat, some will be at correct depth other places not.
@David_Kirtley of course ! Thank you and have a nice week
If you are using upcut mills in thin or flexible materials, this type of pressure plate would help prevent variations in cutting depth as the bit tries to lift the material.
@David_Kirtley , I use a single edge engraving blade to cut two layer plastic sign stock with no lifting and fairly easy setup. I use double sided fiberglass carpet tape to place the sheet and it serves well. I had built a small vacuum table and found the carpet tape works as well with far less expense for various piece sizes.