I've been designing in SP for 14 years. Formerly Datacad.
One of the main features I like is ease of use and fairly rapid learning curve. Modeling is relatively easy and get's the project to good enough to make the sale fairly quickly.
The game changer for me is multiuser capability. I remote share files with a project manager and superintendent who can make changes as needed. This is a huge value add for my team. I don't have to draw everything. Once we get into the build, my team mates can revise the plans as needed instead of sending me the information and me having to make the changes. It's been fairly easy for them to learn the basics, having no previous CAD experience.
My super can walk a job with his laptop and as-built the drawings straight into SP. We used to do paper or .pdf mark ups with me as-builting the drawings. This cuts out a major step and duplication of data entry. It's been a huge productivity multiplier.
We're also using QR Tiger to upload the plans to a unique GR code on the job site so every sub has instant access to the latest plans with all changes along the way. We set up unique QR's for plumbing, electricians, appliance specs, cabinets, changes, siding, and whomever else we think needs an abbreviated set. This allows any sub to fast download just what they need to their cell phones or tablets.
We also use BuilderTrend for project and client management, another very important part of our operation. We're practically paperless. Digital Design-Build. SoftPlan has become a very important part of our operation.