Sequence Scan vs. Index scan

Hi guys,

I'm trying to figure out when Sequence Scan is better than Index Scan. I
just want to know this because I disabled the sequence scan in
postgresql and receive a better result. :)

Two tables.

Table 1 (1 million rows )
-----------
id
text
table2_id

Table 2 (300 thousand rows)
----------
id
text 2

When I join these two tables I have a sequence_scan. :(

Thanks in advance.

Fernando Lujan