System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: Quadro K3100M/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 425.25

Blender Version
Broken: version: 2.82 (sub 7), branch: master, commit date: 2020-03-12 05:06, hash: rB375c7dc4caf4
Worked: (optional)

Subsurf Modifier slows vertex tweaking
[Applying the Subdivision Modifier to Object results to lagging while tweaking vertex.
In fact tweaking with the Subsurf Modifier on is counterproductive for Polygonal Modeling at this time.
It makes no difference even if the Viewport setting is set to 1.
Tested same procedure with daily build blender-2.83-a24f52c51cff-windows64 (29/03/20)
and got the same result.]

Exact steps for others to reproduce the error
[Loaded model made of verts 36.570 - Faces 36.540 - Tri: 73.080
Added Subsurf Modifier.
Settings: Display Modifier in Viewport - Display Modifier in Edit mode.
Render 2 - Viewport 1 - Quality 2.
Selected the Tweak Tool then selected one vertex to move.
It takes about 4 seconds or more to move a single vertex..]

[Based on the default startup or an attached .blend file (as simple as possible)]