Wander about but don't be copious

expatiate / ik-spey-shee-eyt / verb

1. to enlarge in discourse or writing; be copious in description or discussion: to expatiate upon a theme.
2. Archaic. to move or wander about intellectually, imaginatively, etc., without restraint.

History: 1530–40; < L expatiātus ptp. of ex(s)patiārī to wander, digress, equiv. to ex-  + spatiārī to walk about, deriv. of spatium

Webster's Revised Unabridged Dictionary (1913) expands on the meaning:

(n.)
The act of increasing in size or bulk, real or apparent; the state of being increased; augmentation; further extension; expansion.
  
(n.)
Expansion or extension, as of the powers of the mind; ennoblement, as of the feelings and character; as, an enlargement of views, of knowledge, of affection.
  
(n.)
Diffusiveness of speech or writing; expatiation; a wide range of discourse or argument.
  
(n.)
A setting at large, or being set at large; release from confinement, servitude, or distress; liberty.

A good writer will endeavor to not "increase in size or bulk" but will seek "an enlargement of views, of knowledge, of affection." And endeavor to "release onself from confinement" of thinking.