Using TikZ in your (La)TeX document is great for a number of reasons:
* Fonts and line widths are always correct. It looks really unprofessional when your figures have completely different fonts and line widths to the rest of your document,
* Symbolic/declarative description of figures. No need to guess or manually calculate where an equidistant point is or how to draw an arrow between two points, you can just write it down. Your figure will be perfect, not "close enough",
* Ability to write macros and other stuff you would expect from programming your figures.
* Fonts and line widths are always correct. It looks really unprofessional when your figures have completely different fonts and line widths to the rest of your document,
* Symbolic/declarative description of figures. No need to guess or manually calculate where an equidistant point is or how to draw an arrow between two points, you can just write it down. Your figure will be perfect, not "close enough",
* Ability to write macros and other stuff you would expect from programming your figures.