PSA: You can review ST changes in the Loadout screen before applying the ST changes

If you're wondering how a node, or set of nodes, in the skill tree affects your mech, you can switch to the Loadout screen and review them without having to apply the skill node changes. Armor and structure bonues appear in the individual component sections, weapons changes can been seen by hovering over the equiped weapon, and most other changes can be seen under 'Mech Stats on the Loadout screen, several of the changes will appear. When you switch back to the Skills screen, the changes will still be waiting. You can change them and review on the Loadout screen again, before activating the skill nodes for real.

You can also fill out the skill tree without adding SP. The allocated SP count will be in red and the Apply Changes button will be ghosted out. However, you can switch to the Loadout screen with those skill nodes "active", and see how they affected your mech - without costing SP, XP, or C-bills.

It's not as good as being able to take the changes into the training grounds to see how well they perform, but it's a good way to tell the difference between different node selections.